1. Field of the Invention
The present invention relates to a structure of coupling a heat transfer plate and a gasket, for use in a plate type heat exchanger, to each other.
2. Description of the Related Art
Referring to FIG. 1, a conventional heat transfer plate, for use in various kinds of plate type heat exchangers, is shown in plan view. As shown in FIG. 1, the heat transfer plate 10, made of a thin metal plate, includes: corrugated heat transfer channels 11 formed at the substantially overall surface thereof; and first and second fluid passage holes 12 and 12′ perforated through respective corners thereof at the outer side of the heat transfer channels 11. In use, a plurality of the heat transfer plates 10 are closely stacked one above another so that first and second heat exchanging fluids, i.e. a first heating or cooling fluid and a second fluid to be heated or cooled, are able to alternately flow between the stacked heat transfer plates 10. For this, a gasket 20 is inserted in a gasket groove formed at a respective one of the heat transfer plates 10. The gasket groove is formed along the outer circumference of the first and second fluid passage holes 12 and 12′ and the heat transfer plate 10.
Thereby, the gasket 20 is inserted along the outer circumference of the first and second fluid passage holes 12 and 12′ and the heat transfer plate 10 and, then, a plurality of the heat transfer plates 10 are closely stacked one above another. In this case, by allowing the first and second fluid passage holes 12, located at opposite sides of the heat transfer plate 10, to be alternately sealed by the gasket 20, a plate type heat exchange, in which the first and second heat exchanging fluids are able to alternately flow through the gaps between the respective heat transfer plates 10, can be manufactured. In the case of the plate type heat exchanger manufactured as stated above, the corrugated heat transfer channels 11, which are closely formed at the heat transfer plate 10 made of a thin metal plate, act to forcibly create a turbulent flow of the fluids, achieving a great increase in the heat transfer coefficient of the heat exchanger. Specifically, the heat transfer efficiency of the plate type heat exchanger can be increased three fold that of conventional multi-tube type heat exchangers. The increased high heat transfer efficiency, furthermore, enables a reduction in the size and weight of the heat exchanger. Thus, the plate type heat exchanger has been widely applied in the heat exchanger field of various facilities including ships, and the demand thereof has been grown by leaps and bounds.
However, in spite of the above described many advantages, the plate type heat exchanger is problematic because the seal between the respective heat transfer plates 10 is obtained only using the gaskets 20 made of rubber. In this case, physical and chemical properties of the gasket 20 and the coupling structure and coupling strength of the heat transfer plate 10 and the gasket 20 greatly influence the heat resistance and pressure resistance of the plate type heat exchanger. This heavily restricts the kind, use temperature, and pressure of fluids usable with the plate type heat exchanger.
Among the above mentioned several factors restricting the applicability of the plate type heat exchanger, the coupling structure of the heat transfer plate 10 and the gasket 20 has the largest effect on the pressure resistance of the plate type heat exchanger. Referring to FIG. 2 illustrating the coupling structure of the conventional heat transfer plate and gasket, in a state wherein the gasket 20, having an approximately hexahedral cross section, is inserted in the gasket groove 13 of the lower heat-transfer plate 10, the gasket 20 is pressed downward by a lower surface of the gasket groove 13 of the upper heat transfer plate 10, thereby being coupled with both the heat transfer plates 10.
However, when the heat transfer plate 10 and the gasket 20 are coupled with each other in the above described manner, the gasket 20 is easy to rotate in the gasket groove 13 or to be separated from the heat transfer plate 10. More specifically, if the hardness of the gasket 20 is deteriorated due to usage at high temperature and pressure that is exhibited in a lubricant cooler of ships, an internal pressure P applied in an outward direction of the heat transfer plate 10 causes the gasket 20 to rotate in the gasket groove 13 or to be pushed out of the heat transfer plate 10, resulting in a frequent leakage of fluids. This tends to induce a severe deterioration in the continuous operation property of the heat exchanger, and results in environmental contamination and dangerous large-scale accidents when the heat exchanger is used in a petrochemical plant.
Conventionally, to solve the above problems, an adhesive has been applied to the surface of the gasket 20 so that the gasket 20 is affixed to the gasket groove 13 of the heat transfer plate 10. Alternatively, a certain coupling structure has been provided at the gasket 20 or the heat transfer plate 10 to firmly secure the gasket 20 to the heat transfer plate 10 with an improved coupling strength. The former adhesive coupling manner, however, has several problems, such as corrosion of the heat transfer plate 10 and the gasket 20 by the adhesive, and unintentional chemical actions between the adhesive and heat exchanging fluids. Also, in the case of the latter non-adhesive coupling manner, the coupling structure disadvantageously increases the manufacturing costs of the heat transfer plate 10 or the gasket 20 and complicates the process of fixing the gasket 20 to the heat transfer plate 10, resulting in a deterioration in the overall productivity and price competitiveness of the plate type heat exchanger.